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Two-color, two-photon laser-induced fluorescence experiments were performed to probe the intermolecular interactions within the Ar + I2(E, vE = 0–3) potential energy surfaces. Spectra were recorded using the lowest-energy T-shaped level and an excited intermolecular vibrational level with bending excitation within the Ar + I2(B, vB = 23) potential as intermediate levels to guide the spectral assignments. Progressions of intermolecular stretching and bending levels bound within the Ar + I2(E, vE) potentials were identified, and their vibrational frequencies were determined. The harmonic frequency and anharmonic constant for the bending vibrational mode were determined to be ωe(b) ∼ 34.8 cm−1 and ωeχe(b) ∼ 0.3 cm−1. The frequency and anharmonic constant for the stretching mode were found to be the same as reported previously [V.V. Baturo, et al. Chem. Phys. Lett. 647 (2016) 161], ωe(s) = 37.2(1.1) cm−1 and ωeχe(s) = 1.8(2) cm−1.
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Non-adiabatic dissociation dynamics of Ar⋯I2 (E, v) intermolecular vibrational levels probed using velocity-map imaging
Ion time-of-flight velocity-map imaging was used to measure the kinetic-energy distributions of the I2 ion-pair fragments formed after photoexcitation of Ar⋯I2 complexes to intermolecular vibrational levels bound within the Ar + I2 (E, vE = 0–2) potential energy surfaces. The kinetic-energy distributions of the I2 products indicate that complexes in the Ar⋯I2 (E, vE) levels preferentially dissociate into I2 in the D and β ion-pair states with no change in I2 vibrational excitation. The energetics of the levels prepared suggest that there is a non-adiabatic coupling of the initially prepared levels with the continuum of states lying above the Ar + I2 (D, vD = vE) and Ar + I2 (β, vβ = vE) dissociation limits. The angular anisotropies of the I2 product signals collected for many of the Ar⋯I2 (E, vE) levels have maxima parallel to the laser polarization axis. This contradicts expectations for the prompt dissociation of complexes with T-shaped geometries, which would result in images with maxima perpendicular to the polarization axis. These anisotropies suggest that there is a perturbation of the transition moment in these clusters or there are additional intermolecular interactions, likely those sampled while traversing above the attractive wells of the lower-energy potentials during dissociation. I2 (D′, vD′) products are also identified when preparing several of the low-lying levels localized in the T-shaped well of the Ar + I2 (E, vE = 0–2) potentials, and they are formed in multiple νD′ vibrational levels spanning energy ranges up to 500 cm−1.
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- Award ID(s):
- 2102241
- PAR ID:
- 10484206
- Publisher / Repository:
- American Institutes of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 159
- Issue:
- 10
- ISSN:
- 0021-9606
- Subject(s) / Keyword(s):
- Electronic coupling, Transition moment, Intermolecular potentials, Van der Waals molecules, Velocity map imaging, Lasers, Intermolecular forces, Photoexcitation, Photodissociation spectroscopy
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0166512
